Semiconductor apparatus having a trench Schottky barrier Schottky diode

ABSTRACT

A semiconductor apparatus having a trench Schottky barrier Schottky diode, which includes: a semiconductor volume of a first conductivity type, which semiconductor volume has a first side covered with a metal layer, and at least one trench extending in the first side and at least partly filled with metal. At least one wall segment of the trench, and/or at least one region, located next to the trench, of the first side covered with the metal layer, is separated by a layer, located between the metal layer and the semiconductor volume, made of a first semiconductor material of a second conductivity type.

CROSS REFERENCE

The present application claims the benefit under 35 U.S.C. §119 ofGerman Patent Application No. 102015204137.9 filed on Mar. 9, 2015,which is expressly incorporated herein by reference in its entirety.

BACKGROUND INFORMATION

The present invention relates to a semiconductor apparatus having atrench Schottky barrier Schottky diode. A semiconductor apparatus ofthis kind in the form of a trench Schottky barrier Schottky diode isdescribed in German Patent Application No. DE 10 2004 059 640 A1, andhas a semiconductor volume of a first conductivity type, whichsemiconductor volume has a first side covered with a metal layer, and atleast one trench extending in the first side and at least partly filledwith metal.

Schottky diodes usually have metal-semiconductor contacts orsilicide-semiconductor contacts. In Schottky diodes, high injection doesnot occur in forward mode, and clearing of minority charge carriers atturn-off is therefore absent. They switch comparatively quickly and withlittle loss. The term “high injection” refers here to a state in whichthe density of injected minority charge carriers approaches the order ofmagnitude of the majority charge carriers.

Schottky diodes have relatively high leakage currents, however,especially at high temperature, with a strong voltage dependence due tothe “barrier lowering” effect. Thick and lightly doped semiconductorsare also generally needed for high reverse voltages, resulting incomparatively high forward voltages at high currents. Power Schottkydiodes using silicon technology are therefore, despite good switchingbehavior, poorly suitable or unsuitable for reverse voltages above 100V.

The semiconductor apparatus according to the present invention differsfrom the existing art, and is notable for at least the fact that atleast one wall segment of the trench, and/or at least one region,located next to the trench, of the first side covered with the metallayer, has a layer, located between the metal layer and thesemiconductor volume, made of a first semiconductor material of a secondconductivity type.

The example trench Schottky barrier Schottky diode according to thepresent invention (hereinafter also referred to as a “TSBS-P” or“TSBS-PN-P” or “diode,” as will be further explained below) makespossible a comparatively low forward voltage and comparatively lowswitching losses. The comparatively thin layer of the firstsemiconductor material of the second conductivity type furthermoreenables additional shielding of a Schottky contact constituted by use ofthe metal layer. The result is that reverse currents can be appreciablyreduced, in particular at high temperature, while forward voltages andswitching losses remain comparatively low.

The layer, disposed in this fashion, made of the first semiconductormaterial enables particularly low forward voltages in the range of highcurrent densities as compared with conventional high-voltage Schottkydiodes, since the conductivity of the semiconductor volume is greatlyelevated by high injection. This advantage can be further enhanced byway of an integrated PN diode. In addition, the layer, disposed in thisfashion, made of the first semiconductor material results incomparatively low leakage currents thanks to shielding of the Schottkyeffect with the aid of the trench structure. This is furthermoresuitable for modifications that yield comparatively good robustnessthanks to a voltage-limiting clamping function of an integrated PNdiode.

As compared with conventional high-voltage PiN diodes, the advantage ofa comparatively low forward voltage at high current density is obtainedwith the aid of a suitable Schottky contact barrier height incombination with high injection at high current density. Comparativelylow turn-off losses are also obtained, since in forward mode fewercharge carriers are injected into and stored in the low-doped region asa result of the Schottky contact system (e.g., Schottky contact incombination with a thin p-layer directly beneath the Schottky contact).As compared with further conventional “cool SBD” diodes, lower forwardvoltages at high current density occur thanks to more intense highinjection, and lower leakage currents are obtained as a result ofeffective shielding of the Schottky effect.

As compared with a conventional TSBS or TSBS-PN not having asemiconductor layer disposed in this manner (located, for example, as athin p-layer directly beneath the Schottky contact), particularly lowleakage currents are obtained along with a lower forward voltage at highcurrent density, with somewhat higher turn-off losses. In embodimentshaving an integrated PN diode, particularly low leakage currents areobtained with almost the same forward voltage at high current density,and almost identical turn-off losses.

Advantageous embodiments are described below and are shown in thefigures. The features can be advantageous both in isolation and invarious combinations even though further reference thereto is notexplicitly made.

It is possible to embody the diode according to the present invention insuch a way that a breakdown voltage of the diode is, for example, higherthan 10 volts, in particular higher than 100 volts, in particular higherthan 200 volts, or in particular even higher than 600 volts. TheSchottky diode according to the present invention is thus suitable inparticular for high-voltage utilization, and at the same time has a lowforward voltage, a low leakage current, and low switching loss, and ishighly robust. The Schottky diode according to the present invention canfurthermore advantageously be used in particular as a power diode forinverters, for example for photovoltaics or automobile applications. Forexample, the diode can also be used as a so-called “freewheeling” diode.

In an embodiment of the semiconductor apparatus, the semiconductorvolume has at least two trenches. The advantageous properties of thetrench Schottky barrier Schottky diode can thereby be further improved.

Provision can furthermore be made that the first semiconductor materialof the second conductivity type has a layer thickness in a range from 10nm to 500 nm. Provision can moreover be made that a doping concentrationof the first semiconductor material of the second conductivity type isin a range from 10¹⁶ atoms per cubic centimeter to 10¹⁷ atoms per cubiccentimeter. Thin layers of this kind, in particular together with thedoping concentration indicated, are particularly suitable for enabling acomparatively low reverse current, a comparatively low forward voltage,and comparatively low switching losses for the diode according to thepresent invention.

In an example embodiment of the present invention, a region of a bottomof the at least one trench is filled with a second semiconductormaterial, the second semiconductor material being a polycrystallinesemiconductor material of a second conductivity type or a semiconductormaterial of the second conductivity type. This is preferablyaccomplished in such a way that a PN diode is formed by way of thesecond semiconductor material and the semiconductor volume of the firstsemiconductor type. It thereby becomes possible to integrate a PN diode(a so-called “clamping” element) into the semiconductor apparatusaccording to the present invention, electrically in parallel with thetrench Schottky barrier Schottky diode.

In an embodiment of the invention, a breakdown voltage of the PN diodeis lower than a breakdown voltage of the trench Schottky barrierSchottky diode constituted by the metal layer, by the layer of a firstsemiconductor material of the second conductivity type, and by thesemiconductor volume of the first conductivity type.

Preferably, the semiconductor apparatus is embodied in such a way thatan electrical breakdown can occur in a region of the bottom segment ofthe at least one trench.

Preferably, the semiconductor apparatus is embodied in such a way thatit can be operated in a state of breakdown with comparatively highcurrents.

In an example embodiment of the present invention, the region of thebottom of the at least one trench is converted, by ion implantation ofboron (generally: of dopant of a second conductivity type at a higherconcentration than that of the first conductivity type), to asemiconductor material of the second conductivity type. The overallproperties of the semiconductor apparatus can thereby be improved.

Provision can furthermore be made that the trench at least partly filledwith metal has at least two metal plies disposed above one another withrespect to a depth of the trench, an upper metal ply forming a segmentof the metal layer with which the first side of the semiconductor volumeof the first conductivity type is covered, and the metal pliespreferably encompassing different metals. Preferably the at least onetrench is completely filled with at least one metal.

Provision can be made in supplementary fashion that a height of apotential step (Schottky barrier) of the upper metal ply, whichcorresponds to the metal layer, is lower than a height of a potentialstep (Schottky barrier) of a metal ply disposed therebeneath. The resultis to produce a plurality of further advantageous possibilities forimproving the properties of the trench Schottky barrier Schottky diodeand adapting them to particular electrical requirements.

In a further example embodiment of the semiconductor apparatus, a secondside of the semiconductor volume, which is located oppositely facingaway from the first side covered with the metal layer, is covered withan electrically conductive contact material, and a partial volume,adjacent to the contact material, of the semiconductor volume is morehighly doped than the remaining semiconductor volume. The partial volumeis, in particular, a so-called “n⁺” substrate (with inverse doping ofthe semiconductor apparatus it is a “p⁺” substrate), as is similarfashion in the related art. The metal layer described above can be usedas a first electrode (anode electrode) and the aforesaid contactmaterial (which preferably is likewise embodied as a metal layer) can beused as a second electrode (cathode electrode). The overall result is todescribe a particularly suitable configuration for the diode accordingto the present invention.

In an example embodiment of the semiconductor apparatus according to thepresent invention, it has solderable electrodes or solderable componentterminals.

In an example embodiment of the semiconductor apparatus, it is embodiedas a press-in diode and has a corresponding housing. Provision can bemade in supplementary fashion that the semiconductor apparatus is anelement of a rectifier assemblage for a motor vehicle.

Provision can furthermore be made that the semiconductor apparatus ismanufactured at least in part using an epitaxy method and/or using anetching method and/or using an ion implantation method. Advantageouspossibilities for manufacturing the semiconductor apparatus according tothe present invention are thereby described.

In a further embodiment of the semiconductor apparatus, a depth of theat least one trench is from 1 μm (micrometer) to 4 μm, preferably isapproximately 2 μm. This configuration yields particularly suitabledimensions, for example, for use of the diode according to the presentinvention for a rectifier assemblage in motor vehicles. For example, anallowable reverse voltage of approximately 600 volts can be achieved forthe diode according to the present invention. A further advantageousconfiguration of the semiconductor apparatus is obtained if a ratio of adepth of the trench to a clearance between each two trenches is greaterthan or equal to approximately 2.

Provision can furthermore be made that the at least one trench hassubstantially a ribbon shape and/or substantially an island shape. Theribbon shape describes a substantially elongated shape (line) and theisland shape describes substantially a concentrated shape, in particulara circular shape, hexagonal shape, or the like. Preferably the trenchhas a substantially rectangular cross section. A bottom of the trenchcan be embodied to be flat or rounded (“U” shape), for examplesemi-spherical.

In a first variant of the semiconductor apparatus according to thepresent invention, the first conductivity type corresponds to an n-dopedsemiconductor material and the second conductivity type corresponds to ap-doped semiconductor material. In a second variant of the semiconductorapparatus according to the present invention, the first conductivitytype corresponds to a p-doped semiconductor material and the secondconductivity type corresponds to an n-doped semiconductor material. Thesemiconductor apparatus is thus suitable in principle for both possiblepolarities.

Provision can furthermore be made that the semiconductor apparatusencompasses a silicon material and/or a silicon carbide material and/ora silicon-germanium material and/or a gallium arsenide material. Theinvention is thus applicable to all usual semiconductor materials.

Exemplifying embodiments of the present invention are explained belowwith reference to the figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified section view through a semiconductor apparatus ofa first embodiment having a trench Schottky barrier Schottky diode.

FIG. 2 is a simplified section view through a semiconductor apparatus ofa second embodiment having a trench Schottky barrier Schottky diode andan integrated PN diode.

FIG. 3 is a simplified section view through a semiconductor apparatus ofa third embodiment having a trench Schottky barrier Schottky diode.

FIG. 4 is a simplified section view through a semiconductor apparatus ofa fourth embodiment having a trench Schottky barrier Schottky diode.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

In all the Figures, the same reference characters are used forfunctionally equivalent elements and values even when embodiments aredifferent. The following abbreviations, among others, are used in partin the description that follows:

-   -   “TSBS” characterizes a trench Schottky barrier Schottky diode        comparable to the related art.    -   “TSBS-PN” characterizes a trench Schottky barrier Schottky diode        having an integrated PN diode as a so-called “clamping” element,        comparable to the related art.    -   “TSBS-P” characterizes a trench Schottky barrier Schottky diode        according to the present invention, a layer (“thin p-layer”)        made of a first semiconductor material (semiconductor material        26) of a second conductivity type being disposed between a metal        layer (metal layer 14) and a semiconductor volume (semiconductor        volume 12).    -   “TSBS-PN-P” characterizes a trench Schottky barrier Schottky        diode according to the present invention, an integrated PN diode        that constitutes a clamping element being present as a        supplement to the “TSBS-P” embodiment.

FIG. 1 shows a first embodiment (TSBS-P) of a semiconductor apparatus 10having a trench Schottky barrier Schottky diode, which has: asemiconductor volume 12 of a first conductivity type, whichsemiconductor volume 12 has a first side 16 covered with a metal layer14 and, in the present case, two trenches 18 extending in first side 16and at least partly filled with metal.

A depth 42 of trench 18 is respectively approximately 2 μm. In furtherembodiments of semiconductor apparatus 10, depth 42 of trench 18 can bebetween 1 μm and 4 μm. A ratio of depth 42 of trench 18 to a clearance46 between each two trenches 18 is approximately 2. In furtherembodiments of semiconductor apparatus 10 this ratio can also be lessthan or greater than 2.

In the present case each of trenches 18 has metal plies 20 and 22disposed one above another with reference to depth 42 (definedvertically in FIG. 1) of trench 18, an upper metal ply 20 forming asegment of metal layer 14 with which first side 16 of semiconductorvolume 12 of the first conductivity type is covered. Preferably metalplies 20 and 22 encompass different metals. In the present case a heightof a potential step (Schottky barrier) of upper metal ply 20, which inthe present case corresponds to metal layer 14, is lower than a heightof a potential step (Schottky barrier) of metal ply 22 locatedtherebeneath. Further metal layers that constitute, for example, asolderable surface can be located (not shown) above upper metal layer14.

As shown in FIG. 1, regions 24, located next to trench 18, of first side16 covered with metal layer 14 are separated by a layer 26, locatedbetween metal layer 14 and semiconductor volume 12, made of a firstsemiconductor material of a second conductivity type. The aforesaidlayer 26 made of the first semiconductor material is comparatively thin.In the present case layer 26 has a layer thickness of approximately 10nm to approximately 500 nm. The layer thickness is, for example,approximately 70 nm. A doping concentration of the semiconductormaterial of the second conductivity type is approximately 10¹⁶ atoms percubic centimeter to approximately 10¹⁷ atoms per cubic centimeter.

As is further shown, trenches 18 are completely filled with the metal ofmetal plies 20 and 22. Alternatively, trenches 18 can also not becompletely filled with metal. All that is necessary is to ensure thatwall surfaces of trenches 18 and a respective bottom 38 of trenches 18are continuously contacted to the respective metal plies 20 and 22.

A second side 30 of semiconductor volume 12, which is oppositely locatedfacing away from first side 16 covered with metal layer 14, is coveredwith an electrically conductive contact material 28. A partial volume34, adjacent to contact material 28, of semiconductor volume 12 is moreheavily doped than the remaining semiconductor volume 12. Preferably theelectrically conductive contact material 28 is a metal. Contact material28 can in turn encompass several metal layers located one above another.

Semiconductor apparatus 10 is manufactured at least in part using anepitaxy method and/or using an etching method and/or using an ionimplantation method. Such methods for manufacturing semiconductorstructures are conventional.

In an example embodiment of semiconductor apparatus 10, the aforesaidfirst conductivity type corresponds to an n-doped semiconductor materialand the aforesaid second conductivity type corresponds to a p-dopedsemiconductor material. Metal layer 14 is part of a Schottky contact andin this case is an anode electrode. Contact material 28 correspondinglyforms an associated cathode electrode.

In a further example embodiment of semiconductor apparatus 10, the firstconductivity type corresponds to a p-doped semiconductor material andthe second conductivity type corresponds to an n-doped semiconductormaterial.

In the present case, semiconductor apparatus 10 is manufacturedsubstantially from a silicon material. In further embodiments,semiconductor apparatus 10 is manufactured from a silicon carbidematerial and/or a silicon-germanium material and/or a gallium arsenidematerial.

FIG. 1 furthermore shows several further dimensions on semiconductor 10labeled with arrows or double arrows, in the form of a width 44 oftrench 18, a thickness or a depth dimension 48 of the lower (in thedrawing) metal ply 22, a thickness or a depth dimension 50 of uppermetal ply 20, and a thickness or a depth dimension 52 of the layer madeof first semiconductor material 26 of the second conductivity type.

FIG. 2 shows a second embodiment (TSBS-PN-P) of semiconductor apparatus10. Supplementing the embodiment of FIG. 1, in FIG. 2 a region 36 of abottom 38 of trench 18 is filled with a second semiconductor material40, second semiconductor material 40 being of the second conductivitytype. Region 36 has a depth dimension 54 likewise identified by a doublearrow.

Second semiconductor material 40 of the second conductivity type andsemiconductor volume 12, disposed therebeneath in the drawing, of thefirst conductivity type yield a PN diode. This PN diode is connectedelectrically in parallel with the trench Schottky barrier Schottky diodeaccording to the present invention. In particular, a doping ofsemiconductor volume 12 is executed in such a way that upon operation ofsemiconductor apparatus 10 with high currents in a forward direction,high injection of charge carriers can occur.

Semiconductor apparatus 10 is configured in the present case, in termsof dimensions, material, and dopings, in such a way that a breakdownvoltage of the PN diode is lower than a breakdown voltage of the trenchSchottky barrier Schottky diode constituted by metal layer 14, by thelayer made of first semiconductor material 26 of the second conductivitytype, and by semiconductor volume 12 of the first conductivity type.

In an example embodiment of semiconductor apparatus 10, secondsemiconductor material 40 is a polycrystalline semiconductor material.In this case bottom 38 of trench 18 is converted from the firstconductivity type to the second conductivity type by ion implantation,for example using the chemical element boron. This likewise results in aPN diode.

As FIG. 2 shows, the TSBS-PN-P is made up of an n⁺ substrate (partialvolume 34), an n-epi layer (semiconductor volume 12), at least twotrenches 18 etched into the n-epi layer, and a metal layer (electricallyconductive contact material 28) on second side 30 (“back side”) of thechip (semiconductor apparatus 10) as an ohmic contact or cathodeelectrode.

Lower region 36 of trenches 18 is filled with p-doped semiconductormaterial 40 (for example, p-silicon) or poly-semiconductor material (forexample, polysilicon), in accordance with depth dimension 54 indicatedin FIG. 2. Trenches 18 are then filled with a lower metal (metal ply 22)in accordance with depth dimension 48, with ohmic contact to the p-dopedsecond semiconductor material 40 (in particular p-doped silicon orpolysilicon) and with Schottky contact to semiconductor volume 12 (n-epilayer), and then covered with an upper metal (metal ply 20). The uppermetal fills a portion of trenches 18 corresponding to depth dimension50, with Schottky contact to the n-epi layer, and likewise serves (likethe lower metal) as an anode electrode. In particular, the doping of then-epi layer is selected so that upon operation with high currents in aforward direction, high injection into it exists.

As in the case of the TSBS-P (see FIG. 1), thin p-layers (firstsemiconductor material 26 of the second conductivity type) correspondingto an “Np” doping concentration are located directly beneath theSchottky contact (metal layer 14). Metal layer 14 forms, on first side16 of semiconductor apparatus 10, not a single Schottky contact as inthe case of the conventional TSBS-PN, but rather a “Schottky contactsystem” as is evident from FIG. 2.

An advantage of the TSBS-PN-P (FIG. 2) over the TSBS-P (FIG. 1) is theadditional clamping function of the integrated PN diode, and robustnessassociated therewith. The voltage-limiting clamping function resultsfrom the fact that the breakdown voltage of the PN diode is lower thanthe breakdown voltage of the Schottky diode. This relative improvement(with PN/without PN) is similar to the result of a comparison of TSBS-PNwith the conventional TSBS.

In the case of both the TSBS-P according to FIG. 1 and the TSBS-PN-Paccording to FIG. 2, regions 24 not only can be present on an “upperside” of semiconductor volume 12 but additionally (as will be shownbelow in the context of FIGS. 3 and 4) can also be disposed onrespective wall segments 56 and/or on the respective bottom 38 oftrenches 18.

Both TSBS-P (FIG. 1) and TSBS-PN-P (FIG. 2) can also have, in an edgeregion of semiconductor apparatus 10 according to the present invention,additional structures to reduce edge field strength. These can be, forexample, lightly doped p-regions, field plates, or similar structurescorresponding to the existing art.

In the interest of simplicity, it is assumed for the followingdescription of functional aspects that the first conductivity type is arespective n-doping, and the second conductivity type is a respectivep-doping. As already described above, the respective dopings canalternatively also be embodied conversely. This also applies to theexemplifying embodiment previously described with reference to theFigures.

As likewise explained in part above, an exemplifying embodiment of adiode according to the present invention encompasses an electricalcontact material 28 (cathode electrode), built thereupon an n⁺ substrateas partial volume 34, built thereupon a n-epi layer (i.e. an epitaxiallyconstructed semiconductor material) as an (in this case, intrinsic)semiconductor material supplementing partial volume 34 to yieldsemiconductor volume 12, preferably at least two trenches 18 implementedin the n-epi layer by etching, and a metal layer 14 constituting part ofa Schottky contact or as an anode electrode on first side 16 ofsemiconductor apparatus 10. Upon manufacture, preferably trenches 18 arefirstly filled up to a definable depth 48 with a first, lower (asdepicted in FIG. 1) metal layer 22 (hereinafter also referred to as“first metal” or “lower metal”) and are then covered with a second metalply 20 (hereinafter also referred to as “second metal” or “uppermetal”). Second metal ply 20 fills trenches 18 preferably up to an upperrim of trenches 18.

The first metal and the second metal are preferably selected so that thesecond metal possesses a lower barrier height than the first metal. Inelectrical terms, the TSBS is thus a combination of two Schottky diodeshaving different barrier heights: a first Schottky diode having aSchottky barrier between the first metal as anode and the n-epi layer ascathode, and a second Schottky diode having a Schottky barrier betweenthe second metal as anode and the n-epi layer as cathode.

If the barrier heights of the two metals are considerably different,then upon operation in the flow direction (“forward direction”),currents flow principally to the upper metal having the lower barrier;the current also flows via the corresponding lateral wall segments oftrenches 18. The effective area for current flow in the flow directionis therefore comparatively large in a TSBS.

In the reverse direction the first metal, with its greater barrierheight, ensures a greater expansion of the space charge zones. The spacecharge zones expand with increasing voltage and, at a voltage that islower than the breakdown voltage of the TSBS, collide with one anotherat the center of the region between two immediately adjacent trenches18. The result is that the Schottky effects responsible for high reversecurrents are shielded, and the reverse currents are reduced. Thisshielding effect is greatly dependent on structure parameters (e.g.,depth 42 of trench 18), on clearance 46 between trenches 18, on width 44of trench 18, and on a layer thickness of the first metal. The extent ofthe space charge zones in the so-called “mesa” region between trenches18 is quasi-one-dimensional, as long as depth 42 of trenches 18 isappreciably greater than the aforesaid clearance 46.

The advantage of a TSBS is the combination of the two metals, whichenables a certain separation of the designs in terms of requirementsrelating to forward voltage and shielding behavior. The forward voltageand the initial value of the reverse current are influencedpredominantly by the second metal (which has a comparatively lowbarrier). The greater a layer thickness of the second metal, the lowerthe forward voltage and the higher the initial value of the reversecurrent.

On the other hand, the first metal (which has a comparatively highbarrier) determines the voltage dependence of the reverse current aswell as the breakdown voltage and the current distribution at highreverse currents. The TSBS therefore offers an opportunity foroptimization by combining the two metals. Both the respective layerthicknesses and the barrier heights of the two metals can be predefinedas parameters.

The diode embodied in this fashion can be improved if (as alreadydescribed above) a PN diode that acts electrically in parallel with theSchottky diode is integrated into semiconductor apparatus 10. Inparticular, so-called “hole injection” can take place. This diode isinitially referred to below as a “TSBS-PN.”

The TSBS-PN likewise encompasses the n⁺ substrate, the n-epi layer, atleast two trenches 18 etched into the n-epi layer, and an electricallyconductive contact material 28 on a second side 30 (as depicted, thelower side or back side) of semiconductor apparatus 10, producing anohmic contact or the cathode electrode. A lower region of trenches 18 isfilled with p-doped silicon or a polysilicon up to a first height (depthdimension 54). Trenches 18 are then filled with a first metal having arespective layer thickness, the first metal having an ohmic contact tothe p-doped silicon or the polysilicon. The first metal also forms aSchottky contact to the n-epi layer and is thus at the same time part ofthe anode electrode. The first metal is furthermore covered with thesecond metal. The second metal fills trenches 18 preferably at least upto the upper rim of trenches 18. In addition, the second metal likewiseforms, in regions of first side 16 adjacent to trenches 18, a Schottkycontact to the n-epi layer, and likewise serves as part of the anodeelectrode.

In electrical terms, the TSBS-PN that is depicted is a combination oftwo Schottky diodes having different barrier heights and a PN diodehaving “p-troughs” disposed on bottom 38 of trenches 18 as an anode, andthe n-epi layer as a cathode. In particular, the doping of the n-epilayer is selected so that upon operation with high currents in theforward direction, high injection of charge carriers into it can occur.

In the TSBS-PN (comparably to the TSBS with no PN diode) currents flowin the forward direction at first, i.e. at an initially comparativelylow voltage in the flow direction, only through the Schottky diode ofupper metal ply 20. As currents rise, forward currents also flowincreasingly through the PN transition, and optionally also through theSchottky diode of lower metal ply 22 (depending on the respectivebarrier height).

The TSBS-PN thus has a trench structure with a Schottky diode and PNdiode connected in parallel. This combination ensures that in forwardoperation the charge carrier concentration in the lightly doped regionis much higher than in a Schottky diode but considerably lower than, forexample, in a PiN diode. An optimization is thus achieved betweenforward voltage on the one hand, and switching losses on the other hand.

In the reverse direction, space charge zones form both at the Schottkybarriers and at the PN transition. This shielding effect is greatlydependent on structural parameters, in particular clearance 46 betweentrenches 18, width 44 of trench 18 or the width of the aforesaidp-trough, a respective proportional layer thickness of the p-dopedsilicon or polysilicon (corresponding to a layer thickness of thep-trough), and the layer thickness of the first metal.

The TSBS-PN additionally offers comparatively good robustness thanks tothe integrated “clamping” function of the PN diode. The breakdownvoltage (BV_pn) of the PN diode is designed so that BV_pn is lower thanthe breakdown voltage (BV schottky) of the Schottky diodes. Thebreakdown preferably takes place at the bottom of the trench, and thebreakdown voltage of a TSBS-PN is determined by BV_pn. A high fieldstrength therefore does not exist in the vicinity of the Schottkycontacts, and in breakdown mode the reverse currents then flow onlythrough the PN transition and not through the Schottky contacts as in aTSBS. The robustness of the TSBS-PN is thus comparable to that of a PNdiode. The TSBS-PN is therefore also suitable, for example, as a Zenerdiode, although the character of a Schottky diode is nevertheless partlyretained, as with a TSBS. A leakage current of the TSBS-PN, inparticular at high temperature, is considerably higher as compared witha PN diode.

A substantial improvement in the trench Schottky barrier Schottky diodeis obtained according to the present invention (as already describedabove) by the fact that at least one wall segment 56 (see FIGS. 3 and 4)of trench 18, and/or at least one region 24, located next to trench 18,of first side 16 covered with metal 14, is separated by the layer,located between metal layer 14 and semiconductor volume 12 in region 24,made of first semiconductor material 26 of the second conductivity type(“TSBS-P” or “TSBS-PN-P”). This can result, compared, e.g., withconventional PiN power diodes, in considerably lower switching losseswith comparatively low forward voltages and, compared with a TSBS orTSBS-PN, in considerably lower reverse currents with comparable forwardvoltages and switching losses.

The comparatively thin p-layer made of first semiconductor material 26of the second conductivity type (for example having an “Np” dopingconcentration), directly beneath the (topmost) metal layer 14 thatconstitutes a Schottky contact, furthermore provides additionalshielding of the Schottky contact. The result is that reverse currentscan be considerably reduced, in particular at high temperature, whilethe forward voltage and switching losses remain comparatively low.Because of the thin p-layer the trench Schottky barrier Schottky diodeaccording to the present invention constitutes overall not just a singleSchottky contact but rather a “Schottky contact system.”

Note: In the present case the “thin p-layer” is spoken of generally inthe singular in order to indicate that in a respective current path,current passes only through exactly one such thin p-layer. It isunderstood here that in particular because of trenches 18, semiconductorapparatus 10 according to the present invention preferably has severalsuch (parallel) thin p-layers that are therefore separated from oneanother by trench or trenches 18.

Example 1

If the aforesaid thin p-layer made of first semiconductor material 26 ofthe second conductivity type is comparatively thick and comparativelyheavily doped, the Schottky contact is then almost completely shielded.Upper metal layer 14 on first side 16 (the “front side”) ofsemiconductor apparatus 10 according to the present inventionconstitutes, with the thin p-layer, an ohmic contact. A resultingsequence of layers disposed on one another, namely upper metal layer 14,the thin p-layer (semiconductor material 26), the n-epi layer, and then⁺ substrate, functions similarly to a PiN diode. Comparatively lowreverse currents do result in this example, but also comparatively highforward voltages at low current density, and comparatively highswitching losses.

Example 2

If, however, the thin p-layer is configured to be thin and issufficiently lightly doped, the thin p-layer is then almost completelytransparent for the Schottky contact.

Metal layer 14 on first side 16 (the “front side”) of semiconductorapparatus 10, having the layer sequence: metal layer 14/thin p-layer(semiconductor material 26)/n-epi layer (semiconductor volume 12), formsa Schottky contact. The layer sequence: metal layer 14/thin p-layer(semiconductor material 26)/n-epi layer (semiconductor volume 12)/n⁺substrate (partial volume 34) then functions comparably to a Schottkydiode, yielding comparatively high reverse currents, comparatively highforward voltages at high current density, and comparatively lowswitching losses.

In the present case the thin p-layer is referred to as “transparent”when it is transparent to minority charge carriers, in the present caseof a p-emitter for electrons. For this, on the one hand the barrier ofthis Schottky contact system (including the thin p-layer), determined bythe doping concentration and the thickness (depth dimension 52) of thethin p-layer, must be low and thin enough that electrons can be injectedfrom the Schottky contact into semiconductor material 26 or intosemiconductor volume 12 (for example, silicon). On the other hand thereshould be very little recombination of the minority charge carriers(electrons) on their path through the thin p-layer; in other words, atransit time of the electrons must be very much shorter than theirminority carrier lifetime.

Example 3

If the thickness and the doping concentration of the thin p-layer aredesigned suitably (in accordance with the invention), importantparameters such as the forward voltages at high current density, reversecurrents, and switching losses can be predefined or optimized. In thiscase, the layer sequence: metal layer 14/thin p-layer (semiconductormaterial 26)/n-epi layer (semiconductor volume 12)/n⁺ substrate (partialvolume 34) functions like a Schottky diode having a partly transparentp-layer. The optimization parameters for the p-layer are its layerthickness (depth dimension 54) and its “Np” doping concentration.

The present invention makes possible in particular a considerablereduction in reverse currents, in particular at high temperature, bygenerating the thin p-layer directly beneath the Schottky contact, withno concurrent perceptible effects on forward voltage and switchinglosses. This means on the one hand that the p-layer should preferably besufficiently thin, and sufficiently lightly doped, that no (or verylittle) hole injection from the p-layer occurs in forward operation, andthe charge carrier distribution thus corresponds substantially to thatof the TSBS. On the other hand, it means that the thin p-layer should becomparatively thick and comparatively heavily doped in order to at leastpartly shield the Schottky contact in the reverse direction. As alreadydescribed above, the p-layer is therefore embodied with a thickness inthe range of 10 nm to 500 nm and a doping concentration in the range of10¹⁶ to 10¹⁷ per cubic centimeter of volume, depending on theapplication requirements.

As also described above, the present invention also encompasses aTSBS-PN diode that, because of the thin p-layer according to the presentinvention, is referred to hereinafter as a “TSBS-PN-P” (trench Schottkybarrier Schottky diode having an integrated PN diode as a clampingelement, having a thin p-layer directly beneath the Schottky contact).

What results for the “TSBS-PN-P” diode, comparably to the “TSBS-P” diodedescribed above, is also that the comparatively thin p-layer made offirst semiconductor material 26 of the second conductivity type (forexample, having an “Np” doping concentration) is disposed directlybeneath the (topmost) metal layer 14 that forms a Schottky contact.Because of the thin p-layer the TSBS-PN-P diode according to the presentinvention correspondingly also constitutes not just a single Schottkycontact but rather a “Schottky contact system.”

To summarize, advantages of the present invention include, for example:

As compared with conventional high-voltage Schottky diodes:

-   -   Particularly low forward voltages in the range of high current        densities are possible, since the conductivity of the lightly        doped region is greatly elevated by high injection. In the        “TSBS-P” embodiment this results from the thin p-layer directly        beneath the Schottky contact. In the “TSBS-PN-P” embodiment it        results additionally from the integrated PN diode.    -   Comparatively low leakage currents thanks to shielding of the        Schottky effect with the aid of the trench structure in        combination with the thin p-layer directly beneath the Schottky        contact. The “TSBS-PN-P” embodiment is moreover comparatively        robust as a result of the clamping function of the PN diode.

As compared with conventional high-voltage PiN diodes:

-   -   Comparatively low forward voltage up to high current density,        with the aid of a suitable Schottky contact barrier height in        combination with high injection at high current density.    -   Comparatively low turn-off losses, since in forward operation        fewer charge carriers are injected into and stored in the        lightly doped region as a result of the Schottky contact system        (Schottky contact in combination with a thin p-layer directly        beneath the Schottky contact).

As compared with a further solution (so-called “cool SBD” diodes) fromthe related art:

-   -   Lower forward voltage at high current density thanks to greater        high injection. Lower leakage currents as a result of effective        shielding of the Schottky effect.

As compared with conventional TSBSs or TSBS-PNs not having a thinp-layer directly beneath the Schottky contact:

-   -   The TSBS-P embodiment enables particularly low leakage currents        as well as a lower forward voltage at high current density, with        slightly higher turn-off losses.    -   The TSBS-PN-P embodiment enables particularly low leakage        currents with almost identical forward voltage at high current        density and almost identical turn-off losses.

FIG. 3 and FIG. 4 show further exemplifying embodiments of semiconductorapparatus 10 according to the present invention. In contrast to theembodiment according to FIG. 1, in the embodiment of FIG. 3 the(comparatively thin) first semiconductor material 26 of the secondsemiconductor type is additionally disposed at least locally on at leastone wall segment 56 of trenches 18 up to a predefined depth (noreference character).

In the example embodiment of FIG. 4, first semiconductor material 26 isadditionally disposed on a respective entire wall surface of trenches 18and on bottom 38 of trenches 18. In FIG. 4 metal layer 14 or metal plies20 and 22 are therefore each immediately adjacent to first semiconductormaterial 26, but not immediately adjacent to semiconductor volume 12.

What is claimed is:
 1. A semiconductor apparatus having a trenchSchottky barrier Schottky diode, comprising: a metal layer; asemiconductor volume of a first conductivity type, the semiconductorvolume having a first side covered with the metal layer, and at leastone trench extending in the first side and at least partly filled withmetal; and a layer that: is arranged between the metal layer and thesemiconductor volume; is made of a first semiconductor material of asecond conductivity type; is provided at least one of: (i) at at leastone wall segment of the trench; and (ii) at at least one region of thefirst side covered with the metal layer, which at least one region isnext to the trench; and has at least one of: a layer thickness ofapproximately 10 nm (nanometers) to approximately 500 nm; and a dopingconcentration of the first semiconductor material of the secondconductivity type of approximately 10¹⁶ atoms per cubic centimeter ofvolume to approximately 10¹⁷ atoms per cubic centimeter of volume. 2.The semiconductor apparatus as recited in claim 1, wherein thesemiconductor volume has at least two trenches.
 3. The semiconductorapparatus as recited in claim 1, wherein the layer of the firstsemiconductor material of the second conductivity type has the layerthickness of approximately 10 nm to approximately 500 nm.
 4. Thesemiconductor apparatus as recited in claim 1, wherein the dopingconcentration of the first semiconductor material of the secondconductivity type is the approximately 10¹⁶ atoms per cubic centimeterof volume to approximately 10¹⁷ atoms per cubic centimeter of volume. 5.The semiconductor apparatus as recited in claim 1, wherein a region of abottom of the at least one trench is filled with a second semiconductormaterial, the second semiconductor material being one of: i) apolycrystalline semiconductor material, or ii) a semiconductor materialof the second conductivity type.
 6. The semiconductor apparatus asrecited in claim 1, wherein the trench at least partly filled with metalhas at least two metal plies disposed above one another with respect toa depth of the trench, an upper one of the metal plies forming a segmentof the metal layer with which the first side of the semiconductor volumeof the first conductivity type is covered, and the metal plies encompassdifferent metals.
 7. The semiconductor apparatus as recited in claim 1,wherein the at least one trench is completely filled with at least onemetal.
 8. The semiconductor apparatus as recited in claim 1, wherein asecond side of the semiconductor volume, which is located oppositelyfacing away from the first side covered with the metal layer, is coveredwith an electrically conductive contact material, and a partial volume,adjacent to the contact material, of the semiconductor volume being morehighly doped than the remaining semiconductor volume.
 9. Thesemiconductor apparatus as recited in claim 1, wherein the semiconductorapparatus is manufactured at least in part using at least one of anepitaxy method, an etching method, and an ion implantation method. 10.The semiconductor apparatus as recited in claim 6, wherein a height of apotential step or Schottky barrier of the upper metal ply, whichcorresponds to the metal layer, being lower than a height of a potentialstep or Schottky barrier of the metal ply disposed therebeneath.
 11. Thesemiconductor apparatus as recited in claim 1, wherein a depth of the atleast one trench being from 1 μm to 4 μm.
 12. The semiconductorapparatus as recited in claim 11, wherein the depth of the at least onetrench is approximately 2 μm.
 13. The semiconductor apparatus as recitedin claim 1, wherein a ratio of a depth of the trench to a clearancebetween each two trenches being greater than or equal to approximately2.
 14. The semiconductor apparatus as recited in claim 1, wherein thefirst conductivity type corresponds to an n-doped semiconductor materialand the second conductivity type corresponds to a p-doped semiconductormaterial.
 15. The semiconductor apparatus as recited in claim 1, whereinthe first conductivity type corresponds to a p-doped semiconductormaterial and the second conductivity type corresponds to an n-dopedsemiconductor material.
 16. The semiconductor apparatus as recited inclaim 1, wherein the semiconductor apparatus encompasses at least one ofa silicon material, a silicon carbide material, a silicon-germaniummaterial, and a gallium arsenide material.
 17. The semiconductorapparatus as recited in claim 1, wherein the layer thickness of thelayer made of the first semiconductor material of the secondconductivity type is 70 nm.
 18. The semiconductor apparatus as recitedin claim 1, wherein the layer made of the first semiconductor materialof the second conductivity type is arranged below the metal layer and ontop of a face of the semiconductor volume in which there is a respectivehole forming an entrance into a respective one of the at least onetrench.
 19. The semiconductor apparatus as recited in claim 1, whereinthe at least one trench includes at least two trenches, and for each ofat least one pair of adjacent ones of the at least two trenches, thelayer made of the first semiconductor material of the secondconductivity type extends from an edge of one of the pair of trenches toan edge of another of the pair of trenches.
 20. The semiconductorapparatus as recited in claim 1, wherein, below the metal in the trench,the trench further includes therein a second semiconductor material ofthe second conductivity type.
 21. The semiconductor apparatus as recitedin claim 6, wherein each of the metal plies extends across an entirewidth of the trench.